If the bolts would go in straight for 3 full turns how did they then get crossed? I suspect they weren't quite straight when they started. Ive spun wrenches for years so I have a pretty good idea what makes something cross thread........putting them in crooked.
I didn't say they went in straight, I said they went in easily. The engine has to be mounted at an angle, and the header comes off the engine at a different angle.
The screws would go in at what appeared OK, then would bind after several turns, and it would be apparent that they were crooked. The fact that the header is a bolt-on rather than bolt-through design means a ball driver is necessary to install the rear bolt, and telling if it is straight is a matter of feel.
Leonard